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The Mountain Bluebird is one of the most sublime of all North American passerines. Like other North American bluebirds, it is beautiful, bold, and charismatic, with a dedicated human following. Indeed, many people view bluebirds as emblematic species representing all that is good in the world.
The facts are somewhat different. Mountain Bluebirds and their congeners are opportunistic birds that reap huge increases in their populations when people clear forests, raise grazing livestock, and erect nest boxes. And they suffer correspondingly huge declines in their populations when people manage entire landscapes (such as by fire suppression) for other purposes.
Like other bluebirds, the Mountain Bluebird readily accepts nest boxes, making this species not only popular with people but a good subject for field research because its nesting locations and population sizes can be easily manipulated. An attraction to nest boxes, however, also makes this species vulnerable to human-associated hazards such as pets, vandals, and dense rodent populations. Most of what is known about bluebirds, including this species, is based on studies of nest-box populations, not natural ones.
The Mountain Bluebird is probably the most aberrant of all thrushes. It nests in cavities, a habit shared by few other thrushes, and it lives in habitats far more open than those occupied by most other thrushes, including other bluebirds. It eats more insects than most other thrushes, has an unusually large degree of sexual dimorphism in its foraging behavior, and frequently hovers while foraging. In its behavioral ecology, in fact, it resembles not so much a thrush, or even other bluebirds, as it does a scaled-down version of an American Kestrel (Falco sparverius).